gc best practices & troubleshooting · gc best practices & troubleshooting. page 2...
TRANSCRIPT
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Group/Presentation Title
Agilent Restricted
Month ##, 200X
GC Best Practices & Troubleshooting
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Page 2
Troubleshooting Tips
1. Isolate the problem.
(Blank Runs, Inject Un-retained Compound, Know what it is not)
2. Change only one variable at a time.
3. Compare before/after chromatograms.
(Peak shape, response, retention, baseline rise, background, look for trends, etc.)
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Page 3
4. Make sure it makes sense to do what
you’re doing…
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5. Be careful of distractions
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6. Sometimes just a fresh set of eyes is all that is
needed.
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INJECTOR – contamination, flow settings, flow path issues,
overload, valve settings, faulty consumables
COLUMN – contamination, flow settings, flow path issues,
damage (activity & bleed), breakage
DETECTOR – contamination, flow settings, flow path issues,
electronics
What Can Possibly Go Wrong?
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Troubleshooting Starts with Isolating the problem
There are 5 basic areas from where the problem arises
FLOW
INJECTOR
COLUMN
DETECTOR
ELECTRONICS
(Temperature)
But of course it can always be some COMBINATION
Knowing what can & can’t cause the symptom is the key
Logical Troubleshooting
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Column
FlowController
Regulators
Air
Hyd
rog
en
Ca
rrie
r G
as
Mol-SieveTraps
Fixed
Injection
Port Detector Electrometer
Recorder/Integrator
Restrictors
Cylinders or Generators
Typical Gas Chromatographic System
Selection of
type and
velocity
influences
efficiency and
retention time
Page 8
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van Deemter Curves
10 20 30 40 50 60
0.25
0.50
0.75
1.00
u (cm/sec)
h
He
N2
H2
Page 9
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Introduction to Capillary GC
Agilent Restricted
February 11, 2009Page 10
CARRIER GAS
Type Velocity Range (uopt – OPGV)
Nitrogen 8-16
Helium 20-40
Hydrogen 30-55
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Gas Clean Filters
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Column
FlowController
Regulators
Air
Hyd
rogen
Carr
ier
Gas
Mol-Sieve
Traps
Fixed
Injection
Port Detector Electrometer
Recorder/Integrator
Restrictors
Cylinders or Generators
Typical Gas Chromatographic System
Have to be able to
get things to their
gas state
Key to starting the
Chromatographic
process right.
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Influence of Injection Efficiency
Short
Concentrated
Long
Diffuse
Solute Bands
Same column, same chromatographic conditions
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Group/Presentation Title
Agilent Restricted
Month ##, 200X
Injectors
Split
Splitless
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Group/Presentation Title
Agilent Restricted
Month ##, 200X
Septumpurge
Split vent
Split InjectorFlow Path
Carrier gassource
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Group/Presentation Title
Agilent Restricted
Month ##, 200X
Splitless InjectorPurge Off At Injection
Flow through injector = Column flow only
Carrier gassource Septum
purge
Split vent
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Group/Presentation Title
Agilent Restricted
Month ##, 200X
Splitless Injector Purge On After Injection
Flow through injector = Column flow + Split Vent Flow
Carrier gassource Septum
purge
Split vent
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Group/Presentation Title
Agilent Restricted
Month ##, 200X
Split InjectorMajor Variables
Split ratio - determines amount of sample onto column and efficiency of injection (sensitivity vs peak shape)
Liner - influences efficiency of vaporization/discrimination
Temperature - hot enough to vaporize sample without degradation or causing backflash
Injection volume - typically 1-3uL, increasing it does not have as much of an effect as one might think
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Group/Presentation Title
Agilent Restricted
Month ##, 200X
Split Liners – What’s What?
Straighttube
Straighttube withglass wool
Invertedcup
BaffleFixed glass
wool
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Group/Presentation Title
Agilent Restricted
Month ##, 200X
Split Liner
C10
C40
C10
C40
Packed with Glass Wool
Without Glass Wool Packing
Peak Area Ratio
n-C40/n-C10 = 0.64
Peak Area Ratio
n-C40/n-C10 = 0.37
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Group/Presentation Title
Agilent Restricted
Month ##, 200X
Split Liner
C10
C40
C10
C40
Packed with Glass Wool
Without Glass Wool Packing
Peak Area Ratio
n-C40/n-C10 = 0.64
Peak Area Ratio
n-C40/n-C10 = 0.37
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Group/Presentation Title
Agilent Restricted
Month ##, 200X
Splitless InjectorOverview
Most of the sample is introduced into the column
Used for low concentration samples
Wider peaks are obtained than for split injections
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Group/Presentation Title
Agilent Restricted
Month ##, 200X
Splitless InjectorMajor Variables
Purge activation time - determines amount of sample onto column and efficiency of injection (sensitivity vs peak shape)
Liner - preventing backflash more critical than vaporization properties (double tapered type recommended)
Injection volume - typically 1uL or less (backflash)
Temperature – long residence times allow for lower temps
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Group/Presentation Title
Agilent Restricted
Month ##, 200X
Splitless Injector Liners
Straighttube
Bottomrestriction
Dualrestriction
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Solvent Vapor Volume Calculator
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Backflash (carry-over) can give false positives!
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Cleaning the Split/Splitless Injector
Ace
toneMeCl2
Injector body
Remove column,
reducing nut, gold seal,
washer and liner
Carrier gas flow off
GC Off
Disconnect split vent line
Replace split vent trap
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Finding the Split Vent Trap
Follow the split vent line back to the EPC
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Finding the Split Vent Trap
Remove cover at Split Vent
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Replacing the Split Vent Trap
Finger Tight Knurled Nut
G1544-80530
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Split Vent Trap Changed (Column Bleed?!?)
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Before
After
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Group/Presentation Title
Agilent Restricted
Month ##, 200X
Pulsed Splitless
- sample containment more critical than in split injection
- much sharper peaks than in traditional splitless injection
Pulsed Split
- the most volatile components and solvent effected most
- faster sample transfer not as critical since it’s already fast
Split/Splitless Pulsed Injection
Pressure Pulse contains sample expansion
and transfers analytes to the column faster.
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Select Pulsed Splitless Mode in Inlets
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Check the Splitless Pressure
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Double or Triple the Pressure for ~1 sec less than
the Purge Activation Time
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The BIGGEST Problem in GC is…
There are more things that DON’T go through a GC than DO!
….therefore, don’t inject anything and you’ll never have
problems.
OK, inject, but realize that everything just got dirty…deal with it!
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Where Does it Get Dirty?
Here
Here
Here
Here
Here
Here
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What Are You Doing!?
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Bonus Peaks or Ghost Peaks
Contamination in INJECTOR or FLOW (carrier gas)
-Contaminated consumables
-Carryover from a backflash or previous sample
-Bad tank of gas or traps have expired
-Septum bleed
*TIP = Run a blank run…it should be blank!
Before After
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Bonus Peaks - Ferrule Contamination
min5 10 15 20 25
pA
18
20
22
24
26
28
FID2 A, (E:\FERRULE\RTKVSPGR.D) FID2 A, (E:\FERRULE\AGLTVSPG.D)
Agilent
Vespel/Graphite Ferrule from a bag
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More “Off-Brand” O-Ring IssuesControlled Substances Analysis, H2 Carrier
Residue on top of
inlet weldment
Problem Resolution:
Agilent Non-Stick Liner O-Ring
p/n 5188-5365, 10PK
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Septa Bleed vs Column Bleed (MSD)
Source of peaks from outside of the column Columns: HP 5MS
30mx0.25mmx0.25um
Oven: 80 to 160C at 25 C/min,
160 to 320 C at 3 C/min(4),
320 to 325 C at 20C/min(4)
Injection: split 100:1; 1ul of 100ng/ul
Detector: MSD (HP-5973)
run at max sensitivity- full scan
4.00 6.00 8.00 10.00 12.00 14.00 16.00 18.00 20.00
Peak height approx. equiv. to 5 ppb of PAH
(actually impurities)
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Septa Bleed vs Column Bleed (MSD)
Source of peaks from outside of the column ELIMINATED
Columns: HP 5 MS
30mx0.25mmx0.25um
Oven: 80 to160 C at 25 C/min,
160 to 320 C at 3 C/min(4)
320 to 325 C at 20C/min(4)
Injection: split 100:1; 1ul of 100ng/ul
Detector: MSD (HP-5973)
run at max sensitivity- full scan
6 . 0 0 8 . 0 0 1 0 . 0 0 1 2 . 0 0 1 4 . 0 0 1 6 . 0 0 1 8 . 0 0 2 0 . 0 0
5 0 0 0 0
1 0 0 0 0 0
1 5 0 0 0 0
2 0 0 0 0 0
2 5 0 0 0 0
3 0 0 0 0 0
3 5 0 0 0 0
4 0 0 0 0 0
4 5 0 0 0 0
5 0 0 0 0 0
T im e - - >
A b u n d a n c e
T I C : P C 2 4 1 N G 1 . DNew Septa Installed
HP Advanced Green Septa
P/N 5183-4594 ( 11 mm)
320 deg
325 deg
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Peak Tailing
INJECTOR or COLUMN is Active
-Reversible adsorption of active compounds
(-OH, -NH, -SH)
FLOW problem - dead volume, obstruction, poor installation, or severe column contamination
Miscellaneous – temperature issues for late eluters, overloading of PLOT columns, co-elution, polarity mismatch between phase, solute or solvent, and some compounds always tail
*Tip = Inject a light hydrocarbon, should not tail unless flow path problem.
Before After
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good cut
bad cut
bad cut
A flat, 90° square cut will be optimal for all connections
Flow Path Matters
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Symptom – Tailing of Active Compounds1. n-Nitrosodimethylamine2. Aniline3. 1,4-Dichlorobenzene-d44. Benzoic Acid5. Naphthalene-d86. Acenaphthene-d107. 2,4-Dinitrophenol8. 4-Nitrophenol9. 2-Me-4,6-dinitrophenol10. 4-Aminobiphenyl11. Pentachlorophenol12. Phenanthrene-d1013. Benzidine14. Chrysene-d1215. 3,3’-Dichlorobenzidine16. Benzo[b]fluoranthene17. Benzo[k]fluoranthene18. Perylene-d12
Sample: 0.5 ng on column loading with ISTD
Column: 20m 0.18mm 0.18µm
Carrier: Helium 37cm/sec, Ramped flow; 0.7ml/min (0.1min) to 1.3ml/min (15ml/min2)
Oven: 35oC (2.5 min) to 80oC (40oC/min), 15oC/min to 200oC, 8oC/min to 275oC (2 min)
Injection: 0.5µl, Splitless, 280oC, purge flow 30ml/min at 0.75 min
MSD: Transfer Line 290oC, Source 300oC, Quad 180oC
2.00 4.00 6.00 8.00 10.00 12.00 14.00 16.00 18.00 20.00 22.00
0
50000
100000
Time (min)
Abundance
1
2
3 56
7
8
10
11
9
12
13
14
15
16
17
18
4
2.00 4.00 6.00 8.00 10.00 12.00 14.00 16.00 18.00 20.00 22.00
0
50000
100000
Time (min)
Abundance
1
2
3 56
7
8
10
11
9
12
13
14
15
16
17
18
4
Page 46
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Solution – Ultra Inert GC Column1. n-Nitrosodimethylamine2. Aniline3. 1,4-Dichlorobenzene-d44. Benzoic Acid5. Naphthalene-d86. Acenaphthene-d107. 2,4-Dinitrophenol8. 4-Nitrophenol9. 2-Me-4,6-dinitrophenol10. 4-Aminobiphenyl11. Pentachlorophenol12. Phenanthrene-d1013. Benzidine14. Chrysene-d1215. 3,3’-Dichlorobenzidine16. Benzo[b]fluoranthene17. Benzo[k]fluoranthene18. Perylene-d12
Sample: 0.5 ng on column loading with ISTD
Column: 20m 0.18mm 0.18µm
Carrier: Helium 37cm/sec, Ramped flow; 0.7ml/min (0.1min) to 1.3ml/min (15ml/min2)
Oven: 35oC (2.5 min) to 80oC (40oC/min), 15oC/min to 200oC, 8oC/min to 275oC (2 min)
Injection: 0.5µl, Splitless, 280oC, purge flow 30ml/min at 0.75 min
MSD: Transfer Line 290oC, Source 300oC, Quad 180oC
2.00 4.00 6.00 8.00 10.00 12.00 14.00 16.00 18.00 20.00 22.00
0
50000
100000
Time (min)
Abundance
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
2.00 4.00 6.00 8.00 10.00 12.00 14.00 16.00 18.00 20.00 22.00
0
50000
100000
Time (min)
Abundance
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
Page 47
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Improved PerformanceImproving the Entire Flowpath
October Agilent
Restricted
48
UltiMetal – TCD,
FPD, NPD/FID Jets
UltiMetal Capillary Flow Technology
Devices, Ultimate Union
UltiMetal Inlet Weldment, Shell
and Transfer Lines
Ultra Inert GC Column
Ultra Inert Gold Seal
Ultra Inert Inlet
Liner
Ne
w
New UltiMetal
FlexiMetal Ferrules
…now from a single supplier
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Page 49
Split Peaks
INJECTOR (poor sample introduction)
-Injecting the sample twice (some how?)
-Mixed sample solvent (polarity difference)
-Sample in syringe needle (manual inject)
INJECTOR (activity)
-Breakdown (not really a split peak, 2 peaks)
-Sample degradation in injector
VOLATILITY
High boilers dropping out on Cold Spots
-Transfer line temps
-Unions or fittings not tracking column temp
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Broad Peaks
Page 50
INJECTOR
-Poor Installation
-Change in settings (temps/flows)
-Poor sample focusing
-Large change in sample concentration
FLOW
-Change in gas velocity
-Constant Flow vs Constant Pressure
COLUMN
-Contamination
-Damaged/old stationary phase
-Reverse Solvent Effect
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Page 51
No Peaks
DETECTOR (not on or not operational)
INJECTOR (not working)
-Plugged syringe/plunger not moving
-Wrong injector (or detector)
-Huge leak/no carrier gas flow (older systems)
NOT the COLUMN Unless…
-Broken column
-No column
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Page 52
Symptom – No Peaks
10 20 30 40 50
14
16
18
20
22
24
26
28
30
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Page 53
Solution - Unplugged Syringe
0 10 20 30 40 50
14
16
18
20
22
24
26
28
30
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Page 54
Peak ResponseAll Change in Size
DETECTOR (response problem)
-Settings or flows changed
-Electronics failing
-Split ratio set incorrectly
-Wrong purge activation time
-Septum purge flow too high
-Injector temperature too low*
INJECTOR
-Leaky syringe
*Tip = Ask is it all of them or some of them, if all then injector or detector
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Page 55
Peak ResponseSome Change in Size
INJECTOR or COLUMN is active/contaminated
-Irreversible adsorption of active compounds (-OH, -NH, -SH)
-Decomposition of sample
-Temperature Change – Discrimination
-Evaporation from sample
*Tip = If only some change, then ask which ones? If active compounds
then activity. If tracks volatility then cold spots or inlet discrimination.
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Group/Presentation Title
Agilent Restricted
Month ##, 200X
Column
FlowController
Regulators
Air
Hyd
rog
en
Ca
rrie
r G
as
Mol-SieveTraps
Fixed
Injection
Port Detector Electrometer
Recorder/Integrator
Restrictors
Cylinders or Generators
Typical Gas Chromatographic System
Picking the appropriate
stationary phase and optimum
dimensions for the column will give the greatest resolution
in the shortest analysis time.
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Page 57
Peak FrontingShark Fin Shaped or Just Slight
COLUMN (contaminated)
-Overload (More pronounced with large solute and phase polarity differences)
INJECTOR
-Poor efficiency (flow/temp)
-Column installation
-Compound very soluble in injection solvent (need retention gap)
-Mixed sample solvent
OTHER
-Co-elution
-Breakdown
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Page 58
Retention Time Shift
2.00
3.25
4.75
2.75
4.00
5.50
INJECTOR
-Change in injection solvent
-Large change in sample concentration
FLOW
-Leak in the septum
-Change in gas velocity
COLUMN
-Contamination
-Damaged stationary phase
-Loss of stationary phase
-Change in temperature
1.75
3.00
4.50
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Constant Pressure vs Constant Flow Retention
C10
C20
C30
C40
C10
C20
C30
C40
Under constant pressure conditions, flow decreases as temperature increases.
(viscosity of a gas increases as temperature increases)
Page 59
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Gas Viscosity vs Temperature
J.V. Hinshaw, Column Connections, LCGC Asia Pacific, 12(2), 1100 (2009).
Page 60
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Page 61
Loss of Resolution
Resolution is a function of separation and peak width
Separation
Peak Width
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Page 62
Loss of Resolution - Separation Decrease
COLUMN
-Different column temperature
-Contamination (more phase?)
-Matrix components co-eluting
-Different column phase?
Separation
Peak Width
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Page 63
Loss of Resolution - Peak Broadening
FLOW
-Change in carrier gas velocity
-Make-up gas
COLUMN
-Contamination
-Phase degradation
INJECTOR (efficiency)
-Settings, Liner, Installation, etc.
Peak Width
Separation
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Page 64
Typical Problems of Optimized Methods becoming
Unoptimized…and the Reason Why.
• Peak Tailing – Flow Path or Activity
• Bonus Peaks – In Sample or Back Flash (Carry Over)
• Split Peaks – Injector Problems, Mixed Solvent
• No Peaks – Wasn’t Introduced, Wasn’t Detected
• Response Changes – Activity, Injector Discrimination, Detector Problem
• Peak Fronting – Overload or Solubility Mismatch, Injector Problems
• Shifting Retention – Leaks, Column Aging, Contamination or Damage
• Loss of Resolution – Separation Decreasing, Peak Broadening
• Baseline Disturbances – Column Bleed, Contamination, Electronics
• Noisy or Spiking Baseline – Electronics or Contaminated Detector
• Quantitation Problems – Activity, Injector or Detector Problems
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Page 65
Quantitation Problems
DETECTOR
-Poor stability (electronics) or Baseline disturbances (contamination)
-Outside detector's linear range or wrong settings
Activity (adsorption) in INJECTOR or COLUMN
INJECTOR
-Technique, settings, conditions
-Syringe worn
OTHER
-Co-elution
-Matrix effects
-Sample evaporation – leaky vials
-Sample decomposition
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Page 66
Baseline Disturbances
Sudden Changes, Wandering, or Drifting
COLUMN or DETECTOR
-Not fully conditioned or stabilized (electronics)
-Contamination
FLOW
-Changes in carrier and/or detector gas flows
-Valves switching, leaks
WANDER
DRIFT
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Page 67
Noisy Baseline
FLOW
-Contaminated gas
-Incorrect detector settings
COLUMN
-Bleed if at high temperature
-In detector flame (poor installation)
MILD
SEVERE
DETECTOR
-Air leak - ECD, TCD
-Electronics malfunction
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Page 68
Spiking Baseline
DETECTOR
-Particles entering the detector
-Random: poor connection
-Regular: nearby "cycling" equipment (electronics)
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Page 69
Remember
Multiple cause and effect
Do not change too many variables at
once
Complete system = Carrier Gas + Injector +
Column + Detector + Data System
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Self-Tightening Column Nuts
Page 70
Video at agilent.com/chem/STnutvideo
• Less wasted time: No retightening
needed after repeated thermal cycles
• Ease of use: Finger-tight,
consistent connections without tools
• Leak Free = Lower column bleed:
Longer column life
Innovative spring-driven piston continuously presses against ferrule
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Self-Tightening Column Nuts
Page 71
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Changes in Column Dimensions, Gas Type or
Velocity Require Changes in Temp Program Rates
Method Translation Software to the Rescue!
Page 72
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Troubleshooting Resources
Online Troubleshooting and Maintenance Videos
http://www.chem.agilent.com/en-US/Technical-Support/Instruments-Systems/Gas-
Chromatography/Pages/troubleshootingvideos.aspx
GC Troubleshooting Guide
http://www.chem.agilent.com/en-US/Products-Services/Instruments-Systems/Gas-
Chromatography/pages/gp6770.aspx
Method Translation Software
http://www.chem.agilent.com/en-US/Technical-Support/Instruments-Systems/Gas-
Chromatography/utilities/Pages/gcmethodtranslation.aspx
Page 73
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Agilent Better GC Connections
www.agilent.com/chem/betterGCconnections
Order the poster… View the video…